Simultaneous visualization of Propionibacterium acnes and Propionibacterium granulosum with immunofluorescence and fluorescence in situ hybridization

• Direct visualization of Propionibacterium acnes and Propionibacterium granulosum in vitro and in skin tissue.
• Differentiation of multi-species populations by 16S rRNA FISH and immunofluorescence.
• Co-localization of P. acnes and P. granulosum in hair follicles in skin biopsies.

Propionibacterium acnes (P. acnes) and Propionibacterium granulosum (P. granulosum) are common skin colonizers that are implicated as possible contributing factors in acne vulgaris development. We have established direct visualization tools for the simultaneous detection of these closely related species with immunofluorescence assay and fluorescence in situ hybridization (FISH). As proof of principle, we were able to distinguish P. acnes and P. granulosum bacteria in multi-species populations in vitro as well as in a mock skin infection model upon labelling with 16S rRNA probes in combinatorial FISH as well as with antibodies. Furthermore, we report the co-localization of P. acnes and P. granulosum in the stratum corneum and hair follicles from patients with acne vulgaris as well as in healthy individuals. Further studies on the spatial distribution of these bacteria in skin structures in various skin disorders are needed.